1. Field of the Invention
This invention relates to bottle closures and more particularly to a bottle neck structure and a plastic cap adapted to fit on said neck with improved sealing capability.
2. Description of the Prior Art
Plastic caps for narrow necked plastic bottles are typically of the type disclosed in U.S. Pat. No. 3,338,446. The caps have a depending thin-walled skirt weakened approximately midway of its length with a circumferential score line so that the portion of the skirt below the score line may be torn off. The cap has two beads which extend circumferentially around the inside of the cap. These beads fit into grooves in the bottle neck and prevent the cap from being removed from the container. When both beads are in place the cap cannot be removed thereby preventing any tampering with the bottle contents. The lower bead is torn away when the lower skirt is removed. This then allows the cap to be easily pried over the upper bead to allow access to the contents. The upper bead remains with the cap thereby allowing the cap to be used repeatedly for reclosure until the contents of the bottle are exhausted.
There are several problems with the plastic caps of the prior art. A major problem is the splitting of the lower portion of the cap when it is forced onto bottle neck. The score line for the tear-away lower section extends diagonally through the lower portion of the cap skirt and terminates at its bottom edge. This score line weakens the skirt and when pressure is exerted in an attempt to push the cap onto the bottle, the skirt often tears along the score line. Bottles with torn skirts must be removed from the packaging line, the cap manually removed and the bottle and contents recycled. This tearing problem, referred to as a cap splitting, is a substantial burden and significantly increases operating expenses.
Another problem with the prior art caps is the difficulty by the consumer in tearing the lower skirt from the cap. The problem is caused, in part, by the manufacturer when it strengthens the score line for the purpose of reducing cap "splitting" as discussed above. By strengthening the score line, the amount of force or "difficulty" required to tear the lower skirt from the cap is proportionately increased.
Another problem existant with the prior art caps is the loose fit of the cap onto the bottle. A tight fit between the cap and the bottle is essential for a good seal. Although the prior art caps could be made to fit more tightly on the bottle, such an improvement would result in a greater number of cap splitting. Thus an improvement in fit or seal is off-set by an increase in split caps and operating costs.
In an effort to eliminate the difficulties encountered with splitting caps a design as shown in U.S. Pat. No. 3,927,784 was developed. This design eliminated cap splitting by eliminating the diagonal score line that extended to the bottom edge of the skirt and instead utilized two parallel circumferential score lines that defined a tear strip for separating the lower skirt from the upper skirt allowing the cap to be removed. This structure was fine for single use bottles but proved extremely costly for reusable bottles since the lower skirt portion had to be manually removed prior to reuse substantially increasing operating cost.
Since a good seal is required between the cap and the bottle, the prior art devices used tight fitting beads that completely filled the groove and formed a high pressure line contact type of seal about the groove. This type of seal made removal of the cap difficult and also added to the skirt splitting problem due to the interference between the larger bead and the widest portion of the neck structure.
A need thus exists for a tamper-proof cap which can be used repeatedly for reclosure, which can be inserted onto the bottles without cap splitting, which can be removed from the bottle by the consumer without great difficulty, which has a tight fit or good seal and which is relatively easy to produce and inexpensive to manufacture.